write() issue during a low level hdd access Post: 302397631

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Top Forums Programming write() issue during a low level hdd access Post 302397631 by sponnusa on Monday 22nd of February 2010 07:30:46 PM

02-22-2010

Registered User

Quote:

Originally Posted by fpmurphy

Just attempting to read a disk sector is completely different than attempting to write a disk sector following by attempting to read the same disk sector. That is why disk vendors have what are typically called low level utilities for bad disk sector scanning and the like.

yep. you are right. For (IDE) PATA / SATA (t13.org) disks there are the ATA / ATAPI standards which specifies how to query the device directly and SCSI has a loads of standards (t10.org) for interfacing with the drives. The ATA part can be easily coded in DOS / FreeDOS with Assembly / C counterparts.

Win32 support is available too for direct querying / interfacing of the devices (with DDK/SDK apis) and device ioctl calls. There are multiple utilities from various HDD vendors which either falls in either of the above two categories (DOS or WINDOWS).

I would like to know if Linux has anything like that? If I call libata calls directly in my program would it allow me to talk to the drive directly? At least for the (IDE) PATA / SATA drives?

Though Linux is programmer friendly, I feel not much control is given to the programmer (well, it also relates to the security feature! Smilie

and unlike windows, where there are many security exploits / overflows when the kernel address space is hacked from user space leading to privilege escalations, and loads of other issues, not to mention BSOD! Smilie

).

I don't know if I am going into a vicious circle of kernel hacking / Linux abuse mode, but I just don't feel some things are right with Linux! Smilie

I certainly mean no offense with my above words and for the great minds here. The above words are purely because of my frustration in trying to get the program to work partially at least if not completely.

Now for update:

I have tried posix_fadvise, but the read / write calls are locking up on the bad sectors as said by you.

I have removed the O_DIRECT and using O_WRONLY mode with posix_fadvise on the handle with POSIX_FADV_DONTNEED flag for the entire device starting from sector 0 to (last sector * 512). Is that the right option to be used?

Is there any timeout option that can be set on the Read / Write operations to say to the program / kernel to move on to the next sector / block based on the timeout (time consumed for the current sector)?

I tried with the FDSET , but i believe it is only for socket descriptors and not for file handles. (So dumb of myself! Smilie

)

Thanks for the replies.

sponnusa

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LEARN ABOUT OPENDARWIN

tcl_access

Tcl_Access(3)						      Tcl Library Procedures						     Tcl_Access(3)

__________________________________________________________________________________________________________________________________________________

NAME

       Tcl_Access, Tcl_Stat - check file permissions and other attributes

SYNOPSIS

       #include <tcl.h>

       int
       Tcl_Access(path, mode)

       int
       Tcl_Stat(path, statPtr)

ARGUMENTS

       char	     *path	(in)	  Native name of the file to check the attributes of.

       int	     mode	(in)	  Mask	consisting  of	one  or  more  of R_OK, W_OK, X_OK and F_OK.  R_OK, W_OK and X_OK request checking
					  whether the file exists and  has  read,  write  and	execute   permissions,	respectively.	F_OK  just
					  requests checking for the existence of the file.

       struct stat   *statPtr	(out)	  The structure that contains the result.
_________________________________________________________________

DESCRIPTION

       As  of  Tcl 8.4, the object-based APIs Tcl_FSAccess and Tcl_FSStat should be used in preference to Tcl_Access and Tcl_Stat, wherever possi-
       ble.

       There are two reasons for calling Tcl_Access and Tcl_Stat rather than calling system level functions access and stat directly.  First,  the
       Windows	implementation	of  both  functions  fixes  some bugs in the system level calls.  Second, both Tcl_Access and Tcl_Stat (as well as
       Tcl_OpenFileChannelProc) hook into a linked list of functions.  This allows the possibility to reroute file access to alternative media	or
       access methods.

       Tcl_Access checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose
       name is pathname.   If pathname is a symbolic link on Unix, then permissions of the file referred by this symbolic link are tested.

       On success (all requested permissions granted), zero is returned.  On error (at least one bit in  mode  asked  for  a  permission  that	is
       denied, or some other  error occurred), -1 is returned.

       Tcl_Stat  fills the stat structure statPtr with information about the specified file.  You do not need any access rights to the file to get
       this information but you need search rights to all directories named in the path leading to the file.  The  stat  structure  includes  info
       regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always
       0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time.

       If path exists, Tcl_Stat returns 0 and the stat structure is filled with data.  Otherwise, -1 is returned, and no stat info is given.

KEYWORDS

       stat, access

Tcl									8.1							     Tcl_Access(3)